This is a relatively common issue.
I see that you have deleted d3d8.dll from your games folder. This may cause the game to *not* recognise your discrete GPU (if you have one) which could result in much worse performance.
Dear all,
from what I can see, using this particular version of the d3d8.dll file, will allow the game to use your dedicated graphics card (thus increasing performance massively), *without* getting rid of flaming projectiles.
Download the file here:
https://github.com/crosire/d3d8to9/releases
I should just add that I've only tested this with the retail version(s) of Rome & Barbarian Invasion (i.e. 1.5 , & 1.6) not the Steam version(s) (1.5.1) of either. So, mileage may vary. But, this is, to this day, the best fix I've found.
-V